Solar power promises to be the primary technology for the transition to a decarbonized supply of energy among the numerous renewable energy sources; it is a resource widely available worldwide. Its utilization has split into two significant technologies based on solar radiation harvesting and transformation into electricity. The first one we are all very aware of and is today the primary renewable source of clean energy: solar photovoltaic (PV). The PV industry has seen significant innovations and has proven its reliability for the production of electrical energy on a global scale.

Far behind in its development and commercialization, the other technology to capture solar energy at large scale is Concentrated Solar Power (CSP). This technology has the ability to store energy and can provide electricity as and when required. This helps reduce the development cost of new power plants. This can be beneficial to meet future demand for electricity. Despite this, the technology is not yet widely deployed, leading to a global cumulative installation of only 6 GW as recorded in 2018.

As the efficiency of heat engines increases with the temperature of the heat source, to achieve this in solar thermal energy plants, solar radiation is concentrated by mirrors or lenses to obtain higher temperatures. The practical effect of high efficiencies is to reduce the plant's collector size and total land use per unit power generated, reducing the environmental impacts of a power plant as well as its expense. In this way, CSP enhances solar energy density and also can provide both electricity and thermal power.

CSP plants contain two parts: one that harvests and transforms solar power into heat and the other that produces electricity from heating energy. All solar thermal power systems have solar energy collectors that capture and focus sunlight onto a receiver. In most types of systems, a heat-transfer fluid is heated and circulated in the receiver and used to produce steam. The steam is then converted into mechanical energy in a turbine, which powers a generator to produce electricity. All CSP plants need to include tracking systems (single or double axis for the collectors to follow the sun), fixed structures does not make sense in term of energy output for CSP.

Solar thermal power systems may also have a thermal energy storage system component that allows the solar collector system to heat an energy storage system during the day, and the heat from the storage system is used to produce electricity in the evening or during cloudy weather.

There are four primary CSP technologies:

1. Parabolic Troughs

Parabolic troughs are the most evolved CSP methods and comprise most existing commercial plants. The parabolic trough is the linear fixation collector composed of a cylindrically curved parabola mirrors, reflecting the sunlight of a tube in the parabola focal line. A fluid (also called heat transfer fluid) passes through the tubular receiver and becomes very hot. Common fluids are synthetic oil, molten salt, and pressurized steam. The fluid containing the heat is transported to a heat engine where about a third of the heat is converted to electricity. Because of its parabolic shape, a trough can focus the sunlight from 30 times to 100 times its normal intensity (concentration ratio) on the receiver pipe, located along the focal line of the trough, achieving operating temperatures higher than 750°F.

Parabolic trough concentrating systems are used in one of the longest operating solar thermal power facilities in the world, the Solar Energy Generating System (SEGS) located in the Mojave Desert in California. The facility has had nine separate plants over time, with the first plant in the system, SEGS I, operating from 1984 to 2015, and the second, SEGS II, operating from 1985 to 2015. SEGS III–VII (3–7), each with net summer electric generation capacities of 36 megawatts (MW), came online in 1986, 1987, and 1988. SEGS VIII (8) and IX (9), each with a net summer electric generation capacity of 88 MW, began operation in 1989 and 1990, respectively. SEGS 3, 4, 5, 6, 7, and 8 all ceased operation in 2021, leaving only SEGS 9 in operation as of December 31, 2021.

In addition to the SEGS 9, the other parabolic-trough solar thermal electric facilities operating in the United States as of December 2021, and their net summer electric generation capacity, location, and year of initial operation are:

• Solana Generating Station: a 296 MW, two-plant facility with an energy storage component in Gila Bend, Arizona, that started operating in 2013
• Mojave Solar Project: a 2275 MW, two-plant facility in Barstow, California, that started operating in 2014
• Genesis Solar Energy Project: a 250 MW, two-plant facility in Blythe, California, that started operating in 2013 and 2014
• Nevada Solar One: a 69 MW plant near Boulder City, Nevada, that started operating in 2007

2. Solar Towers

Solar Towers capture and focus the sun's thermal energy with thousands of tracking heliostats. A tower resides in the center of the heliostat field. The heliostats focus concentrated sunlight on a receiver which sits on top of the tower. Within the receiver the concentrated sunlight heats molten salt to over 1,000 °F (538 °C). The heated molten salt then flows into a thermal storage tank where it is stored, maintaining 98% thermal efficiency, and eventually is pumped to a steam generator. The steam drives a standard turbine to generate electricity. This process, also known as the "Rankine cycle" is similar to a standard coal-fired power plant, except it is fueled by clean and free solar energy.

Central solar tower technology offers two important advantages: Not only can higher main steam conditions be achieved, currently up to 180 bar at 565°C, which significantly increases the efficiency of the water-steam cycle, but also the heated salt can be stored in tanks for periods of up to several hours.

The U.S. Department of Energy, along with several electric utilities, built and operated the first demonstration solar power tower near Barstow, California, during the 1980s and 1990s. In 2021, there were two solar power tower facilities operating in the United States:

• Ivanpah Solar Power Facility: a facility with three separate collector fields and towers with a combined net summer electric generation capacity of 393 MW in Ivanpah Dry Lake, California, that started operating in 2013.
• Crescent Dunes Solar Energy Project a 110 MW one-tower facility with an energy storage component in Tonapah, Nevada, that started operating in 2015.

3. Parabolic Dish

Parabolic-dish solar concentrators are two-axis solar tracking systems focusing solar radiation onto the heat receiver at the center point of the platform collector. Typically the dish is coupled with a Stirling engine in a Dish-Stirling System, but also sometimes a steam engine is used. A solar dish’s concentration ratio is much higher than linear concentrating systems, and it has a working fluid temperature higher than 1,380°F.

There are no utility-scale solar dish/engine projects in commercial operation in the United States.

4. Linear Fresnel reflectors (LFR)

These reflectors use the Fresnel lens effect, which allows for a concentrating mirror with a large aperture and short focal length, they are capable of concentrating the sun’s energy to approximately 30 times its normal intensity. They concentrate the solar-based beam radiation onto a receiver tube mounted on the focal point of the Fresnel mirror and produce high-temperature working media to generate thermal cycle power. These systems aim to offer lower overall costs by sharing a receiver between several mirrors (as compared with trough and dish concepts), while still using the simple line-focus geometry with one axis for tracking. This is similar to the trough design (and different from central towers and dishes with dual-axis). The receiver is stationary, so fluid couplings are not required (as in troughs and dishes). The mirrors also do not need to support the receiver, so they are structurally simpler. When suitable aiming strategies are used (mirrors aimed at different receivers at different times of day), this can allow a denser packing of mirrors on available land area.

No full-scale thermal systems using Fresnel lenses are known to be in operation.

Innovator and Developers Landscape

In the next framework you can find the innovators and developers that have been leading and carrying out these CSP projects worldwide.

Figure 1. Concentrated Solar Power (CSP) innovator landscape. Find the full version here.

CSP Market

In recent years, the global CSP market has recorded to have a growing market share owing to the supportive government policies and incentives to promote clean energy across the globe.

Thanks to this large number of CSP projects, the power plant builders (engineering, procurement and construction (EPC) companies) and component suppliers have successfully worked their way through a learning curve, thereby reducing costs for planning, erection, and components (such as mirror fields and solar fields, boilers and turbine-generator sets, etc.).

Figure 2. The falling costs of CSP, Global ordered capacity all steam turbine manufactures, Source: Siemens AG.

Despite this trend, the view long held in the years from 2012 to 2016 was that competition between photovoltaics (PV) and CSP would ultimately be won by PV due to the enormous rates of PV expansion and the resultant reductions in cost this would bring. This view was also based on the assumption that the problem of energy storage capacity would be solved by batteries. However, it’s plainly evident today that these circumstances have not yet come to pass. The debate furthermore failed to consider that PV brings no rotating machinery serving grid stability – an added benefit that the steam turbine-generator sets of CSP plants do indeed contribute.

Today, a rather different trend is becoming apparent in current projects: the benefits of both CSP and PV are being combined in hybrid power plants. By combining CSP (7 USD cents per kWh with energy storage) and PV (2 USD cents per kWh without energy storage), power is produced at levelized costs of energy on a par with or even less than fossil fuel power plants – and without fossil-fired emissions.

The main example of this hybrid plants is actually the largest CSP plant in the world, based in Morocco. The Noor Power Station is a 510 MW plant which has an additional 72 MW PV system. the entire project is planned to produce 582 MW at peak when finished.

In their Concentrated Solar Power (CSP) Market Report 2019-2029, Visiongain calculates that the concentrated solar power (CSP) market should be around $37.3bn in 2019 and that the overall revenue of the CSP market will increase during the analysis period between 2019 and 2029. This latest in-depth report on the global CSP market describes trends in the market both quantitatively and qualitatively. General conclusions of their forecast regarding costs can be seen in the graph below.

Figure 3. Visiongain's 2019-2029 forecast in their Concentrated Solar Power (CSP) Market Report.

References

• Helioscop. Concentrated Solar Power (CSP) – from niche to winning technology. February 18, 2019.
• Reve. Role of Photovoltaic and Concentrated Solar Power Technologies towards Renewable Energy Generation. January 31, 2022.
• Reve. Concentrated Solar Power explained. March 5, 2022.
• Reve. Current status of concentrated solar power (CSP) globally. July 25, 2018.